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Abstract:

A socketed high pressure gas discharge lamp having a lamp vessel
comprising a space sealed by at least one seal. The discharge lamp
further comprising a socket in which the lamp vessel is mounted with its
seal and fixed with cement. A lamp axis extending through the socket and
through the space of the lamp vessel. The socket is provided with at
least one opening extending axially through the socket from its base side
to its front side. The opening has an annular wall which is either formed
only by the socket or by a combination of both the socket and the seal of
the lamp vessel. Preferably, the opening is located on either side of the
seal.

Claims:

1. A socketed high pressure gas discharge lamp comprising: a lamp vessel
comprising an electric element arranged in a gastight space, said space
being sealed by a seal; a socket in which the lamp vessel is mounted with
said seal, the socket having a base side facing away from the space and a
front side facing towards the space; a lamp axis extending through the
socket and through the space; at least one current conductor extending in
the axial direction through said seal from the electric element to the
exterior; characterized in that the socket is provided with at least one
opening which extends in the axial direction through the socket from the
base side to the front side, and in that the lamp vessel is fixed with
cement with its seal in the socket.

2. A socketed lamp as claimed in claim 1, characterized in that the
socket comprises at least two of said openings.

3. A socketed lamp as claimed in claim 1, characterized in that the
opening has an annular wall which is formed by the socket.

4. A socketed lamp as claimed in claim 1, characterized in that the
opening has an annular wall which is formed by a combination of both the
socket and the seal of the lamp vessel.

5. A socketed lamp as claimed in claim 2, characterized in that said
openings are evenly distributed over the circumference of the socket.

6. A socketed lamp as claimed in claim 5, characterized in that the seal
is a pinch seal, said pinch seal having a width surface and a thickness,
and in that the openings are located on either side of the seal, facing a
respective width surface.

Description:

FIELD OF THE INVENTION

[0001] The invention relates to a socketed high pressure gas discharge
lamp.

[0002] The socketed high pressure gas discharge lamp comprises:

[0003] a lamp vessel comprising an electric element arranged in a gastight
discharge space, said space being sealed by a seal;

[0004] a socket in which the lamp vessel is mounted with said seal, the
socket having a base side facing away from the space and a front side
facing towards the space;

[0005] a lamp axis extending through the socket and through the space;

[0006] at least one current conductor extending in the axial direction
through said seal from the electric element to the exterior.

BACKGROUND OF THE INVENTION

[0007] Such a socketed lamp is known from U.S. Pat. No. 6,578,991B2. In
the known lamp a construction for cooling a lamp vessel is disclosed. In
general, cooling is required for lamps that are operated at relatively
very high temperatures, for example special metal halide lamps, such as
MSR lamps that are used for stage, studio, and theatre lighting. In
particular, cooling is applied to lamp parts that are sensitive to
oxidation, such as electrical current conductors at the location where
they issue from the seals of the lamp vessel to the exterior. Therefore,
in the known lamp a special construction is disclosed that aims at
cooling only the seals. The construction comprises a large air chamber
and a spout. It is a drawback of the known lamp that the construction to
cool the seal is relatively bulky and expensive. Another drawback of the
known lamp is that the cooling construction comprises many parts that
have to be mounted and positioned onto the lamp vessel.

SUMMARY OF THE INVENTION

[0008] It is an object of the invention to counteract at least one of the
drawbacks of the lamp of the type as described in the opening paragraph.
To achieve this, said lamp is characterized in that the socket is
provided with at least one opening which extends in the axial direction
through the socket from the base side to the front side and in that the
lamp vessel is fixed with its seal with cement in the socket. When the
lamp is operated in upright position, i.e. the axis extends in the
vertical direction and the base is above the lamp vessel, the elongated
shape of the opening and the relatively high temperature of the lamp
vessel at its discharge space, causes a natural convection flow of gas,
for example air, alongside the seal. Thus, it is counteracted that the
seal and metal parts issuing from said seal become too hot and hence the
speed of degradation of the seal and/or current feedthrough is reduced.
In other lamp burning positions, for example horizontal or upside-down,
natural convection will not work properly and cooling via a forced flow
can be properly used, for example by using a fan. The desired orientation
of the flow is imposed by the orientation of the opening with respect to
the lamp vessel, i.e. the axial orientation of the opening causes the
flow to pass alongside the seal. It might be sufficient to cool only the
hottest part of the seal, i.e. the side of the seal that is in the upper
position, in case the lamp is operated in the horizontal position, which
can be achieved with the socket having only one opening. Additionally,
cooling of the discharge is enabled likewise. Fixation of the lamp vessel
with cement is a convenient and relatively cheap way of fixation and
avoids use of relatively expensive and relatively complex mechanical
mounting constructions.

[0009] Alternatively, the socket may have two or more openings to enable
two-sided or more circumferential cooling of the seal. To attain uniform
cooling of the seal, the openings preferably are evenly distributed over
the circumference of the socket. The lamp vessel usually is made of
glass, for example hard glass but preferably quartz glass, i.e. glass
with a SiO2 content of at least 95% by weight.

[0010] In an embodiment, the socketed lamp is characterized in that the
opening has an annular wall which is formed by the socket. This has the
advantage of a very robust fixation of the lamp vessel in the socket as
the seal is cemented on all sides via the whole external surface of the
seal that is located inside the socket. Alternatively, an embodiment of
the socketed lamp is characterized in that the opening has an annular
wall which is formed by a combination of both the socket and the seal of
the lamp vessel. By virtue thereof, the socketed lamp has the advantage
of an enhanced cooling efficiency of the seal as parts of the seal that
are located inside the socket are directly exposed to the flow of cooling
medium. The seal can be a collapsed seal or a pinch seal. A collapsed
seal is made in a sealing process in which the glass is softened to a
relatively low viscosity for enabling the glass to contract itself due to
its surface energy and thus to embed the current conductor inside the
glass and to seal the discharge space. A pinch seal is made via a
pinching process during which the pinch blocks shape the softened glass
of a seal portion of the lamp vessel into a pinch seal. The closest
distance between the pinch blocks during the pinching process determines
the thickness of the pinch seal, while the pinch block surface that
contacts the softened glass determines the width of the pinch seal. In
the case of the pinch seal, a preferred embodiment of the socketed lamp
is characterized in that the openings are located on either side of the
seal facing a respective width surface. This has the advantage of
enhanced cooling efficiency as a relatively large area of the pinch seal
is directly exposed to the cooling medium.

[0011] The lamp vessel may be a double-ended lamp vessel, i.e. a lamp
vessel having two, mutually oppositely positioned seals each with a
respective current conductor, or it may be a single ended lamp vessel,
i.e. a lamp vessel with only one seal through which seal all the current
conductors extend.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] These and other aspects of the invention will be further elucidated
and described in the drawing, in which:

[0013] FIG. 1 shows a cross sectional view of a first embodiment of the
socketed high pressure gas discharge lamp according to the invention;

[0014]FIG. 2 shows an elevated top view of the socket of the socketed
lamp of FIG. 1;

[0015]FIG. 3 shows an elevated view of a second embodiment of the
socketed high pressure gas discharge lamp according to the invention;

[0016]FIG. 4 shows a top view of the socket of the socketed lamp of FIG.
3;

[0017]FIG. 5 shows an elevated top view of a third embodiment of a socket
of a gas discharge lamp according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0018] In FIG. 1 a socketed high pressure gas discharge lamp 1 is shown.
The socketed lamp comprises a lamp vessel 2 comprising an electric
element 3 arranged in a gastight discharge space 4, said space being
sealed by a first 5 and a second seal 6. The socketed lamp further
comprises a socket 12 of a high temperature resistant ceramic material,
in this case aluminum oxide, in which the lamp vessel 2 is firmly fixed
with an adhesive compound 19, in this case cement, with said first seal 5
being in a recess 18 of the socket. The socket has a base side 13 facing
away from the space 4 and a front side 14 facing towards the space. A
lamp axis 15 extends through the socket 12, through the first seal 5 and
into the space 4. A current conductor 7 extends axially through said
first seal 5 from the electric element to the exterior. The socket is
provided with two openings 16,17 which extend axially through the socket
from the base side to the front side. The openings 16,17 are separated
from the recess 18 by a respective annular wall 11. The discharge lamp
shown is a MSR Gold 1200 Watt AC lamp of Philips, with a filling of
mercury, a mixture of salts of rare earth metals, and argon as a starting
gas.

[0019] In FIG. 2 the socket 12 of the socketed lamp of FIG. 1 is shown.
The socket has two axially extending openings 16, 17 that are evenly
annularly distributed over the circumference 23 of the socket. Each
opening has an annular wall 11 which is completely formed by the material
of the socket and hence the openings are separated from the recess 18 in
which the lamp vessel is to be mounted with its first seal (see FIG. 1).
Two passages 21,22 in the recess 18 are meant for electric conductors
(see reference numeral 7 in FIG. 1) issuing from the lamp vessel to pass
to the base side of the socket. The socket is made of a glass-ceramic
material having a coefficient of thermal expansion that is about the same
as the coefficient of thermal expansion of quartz glass, i.e. in the
range of 1*10-7 to 1*10-6 K-1.

[0020] The socketed lamp 1 of FIG. 3 shows a lamp vessel 2 fixed with
cement 19 in the socket 12, with parts of the first pinch seal 5 that are
located inside the socket being free from cement and forming part of
annular walls 11 that surround the axially extending openings 16, of
which only one opening is visible, in the socket. The openings are
located on either side of the seal and face a respective width surface 5a
of the seal. As shown in FIG. 4, which is a top view of only the socket
12 of the socketed lamp of FIG. 3, both the openings 16, 17 and the
recess 18 are integral, and are subdivided by the first seal 5 of the
lamp vessel to form the openings 16, 17 in the socket. In this
embodiment, the fixation of the lamp vessel in the socket is somewhat
less robust, but enables efficient cooling of the seal 5 and current
conductors 7 (see FIG. 1) of the lamp, as parts of these components that
are located in the socket are exposed directly to cooling gas flowing
through the openings.

[0021] In FIG. 5 a third embodiment of a socket 12 according to the
invention 1 is shown. The socket has four axially extending openings
16,17,26,27 that are evenly annularly distributed over the circumference
23 of the socket. Each opening has an annular wall 11 which is completely
formed by the material of the socket and hence the openings are separated
from the recess 18 in which the lamp vessel is to be mounted with its
first seal. In

[0022]FIG. 5 the recess 18 is suited for accommodating a lamp vessel
which has a collapsed first seal. In the Figure the socket is made of
sintered aluminum oxide.